The genomes of pathogenic bacteria are being rapidly sequenced. A major challenge is to devise efficient, sensitive, and specific assays to screen bacterial genomes to identify pathogenic proteins and determine their specific roles in pathogenesis. Although yeast cannot serve as a physiologic model of human infection, our laboratory and others have recently established Saccharomyces cerevisiae as a powerful model system to study bacterial proteins that target potentially conserved eukaryotic host cell processes. Preliminary evidence presented in this proposal demonstrates that toxic yeast phenotypes conferred by Shigella proteins are a sensitive and specific screen for proteins that target host cell processes. Given its relatively small genome, genetic tractability, well- developed post-genomic tools, conservation of many basic cellular processes, and the wealth of available systematic data S. cerevisiae is an ideal model organism for multidisciplinary systems- biology studies. In response to PA-02-011, "Bioengineering Research Grants," we propose to develop and validate a multidisciplinary, integrative, systems approach in yeast involving genomics, proteomics, cell biology and novel bioinformatics software development to identify host cell processes targeted by three Shigella proteins, IpgB, OspCI and OspF. Evidence suggests that each of these proteins is delivered directly into host cells during infection, but little is known about their functions within. We hypothesize that the genome-wide screens described in this proposal will result in the characterization of the molecular roles in pathogenesis of each of these proteins. Experiments in this proposal focus on proteins from the genetically manipulable Shigella so that we can relatively easily test hypotheses in physiologic models of disease. However, once optimized, this multidisciplinary approach should be applicable to study any microbial pathogen that targets intracellular host cell processes, especially pathogens that are dangerous to grow or difficult to genetically manipulate like Mycobacterium and Chlamydia. This work is important is relevant to public health issues since by investigations mechanisms that bacterial pathogens used to cause disease, we will gain information that will help develop new antimicrobials to treat these infections. Furthermore, we are interested in developing a new and efficient way to study bacterial pathogens that are dangerous and difficult to study in other ways.